In order to find out the effect of imperfect accommodation of gas molecules at solid boundary on the flow due to thermal stress, the behavior of gas around an arbitrary but smooth shaped body with constant temperature which is placed in an infinite expanse of gas at rest with non-uniform temperature is investigated on the basis of the linearized Boltzmann-Krook-Welander equation and Maxwell type boundary condition for small Knudsen number. A formula for slip velocity due to thermal stress is derived. The slip coefficient is increased as the accommodation coefficient is decreased. A sphere placed in a gas with uniform temperature gradient is taken as an example. The physical mechanism how the flow is induced is also discussed.
A solid spherical particle in an infinite expanse of gas at rest with a uniform temperature gradient is considered. The flow induced around the particle and the thermal force acting on it are investigated on the basis of the asymptotic theory for a slightly rarefied gas. The thermal force is found to be in the direction of the given temperature gradient or in the opposite direction depending on the size and heat conductivity of the particle.
The teflon pulsed plasma microthruster is a kind of electrical thruster and generates cicrothrust pulsatively by using a solid teflon as a propellant. The teflon thruster presented here is the inflight model developed for the operation in the space emviroment. This note reports on the impulse bit measurement of the teflon thruster in the ground. We applied the physical pendulum to the thrust stand and operated the thruster pulsatively once in a cycle when the pendulum passed through the lowest point. A light beem, which was thrown from the outside of vacuum chamber, was reflected on the mirror settled at the fulcrum of pendulum and was recorded on the photo-sensitive paper moving at the constant rate. Each microimpulse bit was integrated during a certain time and the average impulse bit was obtained from the amplitude of pendulum as the function of the discharge energy and the voltage applied to the thruster.